MBA can't connect to Hotspot
Has anybody seen similar behavior and found a solution?

Nope, never seen this before, but I've noticed that the default route is missing in the routing table of the non-working connection. 

The default route is needed so that packets for destinations not listed in the routing table can be properly routed and delivered.

You can fix it by adding the route like this:

sudo route add default &lt;IP address of router&gt;


In your case:

sudo route add default 192.168.182.1


This treats the symptoms, not the disease. To find out what's wrong download dhcpdump from http://www.mavetju.org/unix/general.php, compile it in Terminal:

cd ~/Downloads/
tar xzf dhcpdump-1.8.tar.gz
cd dhcpdump-1.8
make


and run it:

sudo ./dhcpdump -i en0


You'll get an output similar to this:

  TIME: 2014-02-18 10:04:03.832
    IP: 0.0.0.0 (e0:f8:49:27:4e:22) &gt; 255.255.255.255 (ff:ff:ff:ff:ff:ff)
    OP: 1 (BOOTPREQUEST)
 HTYPE: 1 (Ethernet)
(...)
OPTION:  53 (  1) DHCP message type         3 (DHCPREQUEST)
OPTION:  55 (  9) Parameter Request List      
    1 (Subnet mask) 3 (Routers) 6 (DNS server) 15 (Domainname) 
    119 (Domain Search) 95 (LDAP) 252 (MSFT - WinSock Proxy Auto Detect) 
    44 (NetBIOS name server) 46 (NetBIOS node type)

OPTION:  57 (  2) Maximum DHCP message size 1500
OPTION:  61 (  7) Client-identifier         01:e0:f8:49:27:4e:22
OPTION:  50 (  4) Request IP address        10.0.0.31
OPTION:  51 (  4) IP address leasetime      7776000 (12w6d)
OPTION:  12 (  8) Host name                 avallone
---------------------------------------------------------------------------

  TIME: 2014-02-18 10:04:03.934
    IP: 10.0.0.1 (c4:3d:c7:a6:a3:98) &gt; 10.0.0.31 (e0:f8:49:27:4e:22)
    OP: 2 (BOOTPREPLY)
 HTYPE: 1 (Ethernet)
(...)
OPTION:  53 (  1) DHCP message type         5 (DHCPACK)
OPTION:  54 (  4) Server identifier         10.0.0.1
OPTION:  51 (  4) IP address leasetime      86400 (24h)
OPTION:   1 (  4) Subnet mask               255.255.255.0
OPTION:   3 (  4) Routers                   10.0.0.1
OPTION:   6 (  4) DNS server                10.0.0.1


The important part for us is option 3 in the BOOTREPLY packet:

OPTION:   3 (  4) Routers                   10.0.0.1


Is it missing in the answer your Mac gets, or are there other options like static routes (option 33) that might confuse the BSD network stack?

(You could also use sudo tcpdump -i en0 -s 1500 -XX port bootps or port bootpc to analyze the DHCP packets but dhcpdump offers a much more readable output.)

Which is the value of RouterIPAddress in/private/var/db/dhcpclient/leases/&lt;interface&gt;,&lt;count&gt;-&lt;MAC address&gt; when the connection is not working? As an example, this is my DHCP lease file:

&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"&gt;
&lt;plist version="1.0"&gt;
&lt;dict&gt;
    &lt;key&gt;IPAddress&lt;/key&gt;
    &lt;string&gt;10.0.0.31&lt;/string&gt;
    &lt;key&gt;LeaseLength&lt;/key&gt;
    &lt;integer&gt;86400&lt;/integer&gt;
    &lt;key&gt;LeaseStartDate&lt;/key&gt;
    &lt;date&gt;2014-02-21T07:04:53Z&lt;/date&gt;
    &lt;key&gt;PacketData&lt;/key&gt;
    &lt;data&gt;
    (...)
    &lt;/data&gt;
    &lt;key&gt;RouterHardwareAddress&lt;/key&gt;
    &lt;data&gt;
    (...)
    &lt;/data&gt;
    &lt;key&gt;RouterIPAddress&lt;/key&gt;
    &lt;string&gt;10.0.0.1&lt;/string&gt;
    &lt;key&gt;SSID&lt;/key&gt;
    &lt;string&gt;hotspot&lt;/string&gt;
&lt;/dict&gt;
&lt;/plist&gt;


Any clue where the duplicated line got there and how i can get rid of it? And matter of fact, what does it even do?

It looks like your Mac can't properly process the DHCP reply from the router. You can delete the duplicated line with:

sudo route delete -ifscope en0 -net 192.168.182 -link 'link#4'


Since the duplicated routes have the same destination and gateway I don't think they will hinder network functionality, as you can see, only one of them is being used, the one with Refs greater than 0:

192.168.182        link#4             UC              0        0     en0
192.168.182        link#4             UCSI            2        0     en0