OK, I have finally decided to look for the bug which caused Hydra Slayer for Android to freeze and close sometimes (quite often, actually). Apparently the bug was caused because of my misunderstanding of JNI (I didn't know I have to call DeleteLocalRef).
Also the game runs faster now due to an optimization in transferring the screen data from JNI to Android.
For non-Android users, there is just one small bug fixed (auto-explore mode sometimes worked incorrectly).
Download Hydra Slayer for Android from the Android Market, or the PC version here.