Bukkit

What steps will reproduce the problem?
1. Capture a mob/animal with an egg.
2. Take that spawn egg and throw it.

What is the expected output? What do you see instead?
The captured animal should spawn. Instead, only the sounds of the animal can be heard... there is no animal present upon throwing the spawned egg.

What versions MobCatcher, CraftBukkit, and Spout (if any) are you using?
The latest version of MobC and the intended CB 1.7.5 R-03, #3039

Have you previously had any older versions of MobCatcher on your server?

Do you have an error log of what happened?
Neither the console nor the latest logs show anything pertaining to mobcatcher.

Please provide any additional information below.

Sometimes, and it's not consistent - a regular egg will come from throwing the spawn egg. The spawn egg will appear after throwing it, and it literally spawns a regular egg instead of the mob/animal previously captured. :/

The rest of the time, like I said, you can throw the spawn egg, but it just explodes into nothing. MobC in the chat will say that you've successfully spawned something, but there'll be nothing in your screen that resembles that.

On that comment, I meant ", and it's not consistent'

This is the only log information I could find related to this plugin, and it appears to be configured/cooperating correctly with CB.

[16:26:17] [Server thread/INFO]: [MobCatcher] Enabling MobCatcher v3.16
[16:26:17] [Server thread/INFO]: [MobCatcher] Author: Malikk
[16:26:17] [Server thread/INFO]: [MobCatcher] Hooked Vault 1.2.25-b320
[16:26:17] [Server thread/INFO]: [MobCatcher] Spout was not found.
[16:26:17] [Server thread/INFO]: [MobCatcher] signData File is Empty
[16:26:17] [Server thread/INFO]: [MobCatcher] mobData File is Empty
[16:26:17] [Server thread/INFO]: [MobCatcher] Remove stackability: true
[16:26:17] [Server thread/INFO]: [MobCatcher] Starting Plugin Metrics
[16:26:17] [Server thread/INFO]: [MobCatcher] Enabled**

Are you in a protected area, when trying spawn spawn them, by chance?

I'm not able to replicate this issue. Possibly a plugin conflict. Like @SilverKytten said, you might be in an area where something else is stopping mobs from spawning