I think this is a bug in libhyphen 2.8.6: In the following example, this hyphenation is NOT found correctly (in fact, no hyphenation at all: 0000000000):
abendstern --> abend=stern
when the dictionary contains just these two patterns:
If the dictionary contains just the one pattern "2d1s", the correct hyphenation (0002100000) is returned. As far as I understand, the second pattern ("end3sz") should not even match, at least that is what the TeX program patgen thinks. So it should neither inhibit the first pattern ("2d1s").