Why do these Python XTEA implementations require different deltas?
If you take a close look at line 105 of the C++ implementation, you see that it subtracts delta from the sum instead of adding it:

103            for (int32_t i = 32; --i &gt;= 0;) {
104                    v0 += ((v1 &lt;&lt; 4 ^ v1 &gt;&gt; 5) + v1) ^ (sum + k[sum &amp; 3]);
105                    sum -= delta;
106                    v1 += ((v0 &lt;&lt; 4 ^ v0 &gt;&gt; 5) + v0) ^ (sum + k[sum &gt;&gt; 11 &amp; 3]);
107            }


Since $\textrm{0x61C88647+0x9E3779B9}=2^{32}$, this is equivalent to adding the "normal" delta.

A rather odd design choice, if you ask me, but it works.