Until recently, fiber Bragg gratings have been found to exhibit three different growth mechanisms, type I, type II-arising from physical damage-and type IIA. Recently, it has been reported a new regime termed type IA. In this contribution we will report the observation of an abnormal growth mechanism of gratings written in high-Germanium-doped fibers, different from the referred types. First, we will identify possible causes for the observed evolution of the induced perturbation's characteristics (mean value and amplitude) as a function of the accumulated UV fluency. Then, we will analyze the thermal behavior (stability and sensitivity) of gratings formed through the referred abnormal mechanism and compare it with the obtained for the other well-known types (type I, IA and IIA), discussing the results and possible applications in sensing and optical communications areas.