I have been practicing agile for more than a year now. As part of our sprint, some times we will have Investigation Tasks. We skip poker planning for theses tasks, and adds blanket numbers.
Theses are tasks like investigating some tricky defects or technical feasibility of some features etc..
Is this proper or is there any alternative ways to tackle it?
If, when you say "skip poker planning for these tasks and adds blanket numbers", you mean that you time-box them, then you are talking about a regular practice in scrum called a Spike:
A spike is an experiment that allows developers to learn just enough about something unknown in a user story, e.g. a new technology, to be able to estimate that user story. A spike must be time-boxed. This defines the maximum time that will be spent learning and fixes the estimate for the spike.
We call these stories "Spikes" and allocate up to three days to each. Once the time is up work stops on the spike and the findings are discussed in the team. Based on those discussions the team then decides about the next steps.
Typically we use spikes for tricky tasks as you call them such as new technologies, new designs, challenging bugs, performances issues, trialing new tools, user interface prototypes, and many more. This list is far from complete.
We create a spike when we are unsure about the content or size of a particular item. In other words the item comes with a lot of uncertainty. We use the spike to reduce or eliminate the uncertainty.
So in that sense I think you use them the "proper" way. You just use a different label for this type of task than we do.
There is no such thing as agile police that are going to come to your office and arrest you for not following an implementation of the methodology exactly to the letter. If having investigation tasks is working for you there is no reason to change it because someone wrote a paper or a book that says differently.
