I found solution to the bug related to getblocktemplate mining method.
New version of wallet, with this bugfix and other upgrades, will be released in few days for Windows, OS X and Linux.
Will this be released soon?
I decided to take better approach and I instead modified cpuminer. It took some time, because I'm not familiar with cpuminer code (and it wasn't written with code clarity as goal), but here it is.
This problem was caused by implementation of BIP 34 in Bitcoin. When BIP 34 was implemented, block height was already quite high, so nobody noticed this bug that affects only blocks in range 32767-65536. Wallet would like the signature to be 3 bytes long, even when 2 bytes would be enough. But since we are using getblocktemplate in LemonCoin since start, this bug affected us.
Repo:
https://github.com/withthelemons/cpuminer-multi/Download:
https://github.com/withthelemons/cpuminer-multi/releasesPM me if you have any issues.