Safety question about a safety.

[sprout]

I recently purchased a full-sized steel witness with a single-sided safety on consignment. I ordered an ambi safety from Henning (who was great). When I installed the new safety--which is the outer limits of my gunsmithing skills--I noticed something odd. As before, the safety blocks the trigger when I engage the safety, and the hammer stays cocked when I rack the slide. So far, so good. However, when I thumb-cock the hammer, it doesn't stay cocked. If I cock the hammer, hold it back, engage the safety, and then disengage the safety, it does stay cocked. Is this normal, or more importantly, is it safe?

Thanks

[sprout]

I recently purchased a full-sized steel witness with a single-sided safety on consignment. I ordered an ambi safety from Henning (who was great). When I installed the new safety--which is the outer limits of my gunsmithing skills--I noticed something odd. As before, the safety blocks the trigger when I engage the safety, and the hammer stays cocked when I rack the slide. So far, so good. However, when I thumb-cock the hammer, it doesn't stay cocked. If I cock the hammer, hold it back, engage the safety, and then disengage the safety, it does stay cocked. Is this normal, or more importantly, is it safe?

Thanks

I have some additional information, if it helps. The hammer will thumb-cock with the slide off. It will also thumb-cock with the slide pulled back 0.3 inches.

Any ideas? Can I test fire it safely?

Thanks