while adding a new dial, another random one gets deleted

i am using FF69 64bit and i have several groups in speed dial. sometimes it happens that i add a new dial, but as soon as i click ok, the dial is added but another random one is deleted (in the same group or in another group). i have to use local backup to restore the dials and try again. sometimes it works as it should, but it seems to be random.

i couldnt find out when it works and when not. no ideal how to provide futher information. but this bug really is annyoing