Discrete H-Bridge very low current output
Design 1 wouldn't be my first thought on how to do this either! The transistors aren't a great choice, but are cheap &amp; common.

The layout here is more conventional, and you can physically link 1-2, &amp; 3-4 to connect to your arduino without the risk of short circuits.

I suspect your code may be setting both lines high together - the only advantage I can see to the posted circuit is that this does not necessarily cause smoke (but may well do as you describe). This is why posting the code is recommended!